The present invention relates to silicone polymer fluids that are useful as hydraulic fluids and more particularly the present invention relates to silicone polymer fluids where a substantial portion of the substituent groups on the silicon atoms are alkoxy groups and various other types of alcoholic substituent groups which groups are attached to the silicon atoms.
Most brake fluids that are presently sold are basically glycol based polyethers which vary from case to case depending on the type of polyether units and the number of polyether units in the polymer chain. Although such brake fluids have found wide acceptance and usage in vehicles and particularly automobiles, such glycol base fluids have various disadvantages so that various automobile manufacturers have sought to obtain a better quality of brake fluid so that such brake fluid when inserted into the brake system of an automobile would provide a higher factor of safety.
One of the disadvantages of such glycol based polyether brake fluids is that it has a rather limited high temperature stability. Thus, it has been found that at some temperatures to which the brake system of an automobile may conceivably be exposed to, the brake fluids presently on the market might degrade or evaporate. It has also been found that at such high temperatures which the brake system of an automobile might be exposed to that the brake fluids presently on the market might possibly vaporize, causing spontaneous brake failure. Thus, the brake fluids presently on the market tend to have an undesirable low boiling point.
Another disadvantage of the glycol based polyether brake fluids presently on the market is that they are hygroscopic, that is, such fluids tend to pick up water and moisture from the air quite easily. Although such glycol based polyether brake fluids have the property of being compatible with large amounts of water, nevertheless, due to their hygroscopicity they will over a period of time absorb a large amount of moisture into the system, such that when the compatibility level of the water in the polyether glycol based fluid is exceeded the water will cause undesirable changes in the physical properties of the brake fluid. At low temperatures such large amounts of absorbed water in the polyether glycol based brake fluid will undesirably increase the viscosity of the brake fluid and deleteriously affect the performance of the brakes. At high temperatures the presence of large amounts of water may result in the water being vaporized to create what is known as vapor-lock in the hydraulic lines of the brake system, which also results in improper performance of the brakes.
To meet these disadvantages of the brake fluids presently on the market, manufacturers have looked at other types of fluids that would have a higher performance factor in automobile brake systems and particularly have looked to brake fluids that would not have the disadvantages of the glycol based poyether brake fluids which are mentioned above.
Several silicone fluids have been proposed for use as brake fluids. Silicone fluids have the particular advantage of a very high flash point and do not degrade and thus retain their chemical stability at high temperatures. In addition, silicone fluids have a high fire point such that even during periods of exceptional stress in the operation of the brake hydraulic system of an automobile the temperature that is reached in the hydraulic system is considerably below the flash point and fire point of such silicone fluids. In addition, silicone fluids have the additional advantage that they have a desirably low viscosity at low temperatures even at temperatures as low as -40.degree. C. In addition, most silicone fluids are not hygroscopic such that they take up very little water or moisture from the air and thus are not usually bothered with the problems of excessive water pick-up. However, it has been envisioned that water by some means or other may by accident enter into the hydraulic system so that it is desirable that a silicone fluid be compatiable with a reasonable amount of water, that is, the water can be absorbed into the silicone fluid. In addition, it is desirable to obtain a silicone fluid which has as low viscosity as possible at a low temperature, say, of -40.degree. C and yet have a minimum viscosity at high operable temperatures.
The necessity for such a desirably low viscosity of the brake fluid at low temperatures, say, as -40.degree. C is so that such a fluid can be used in very cold climates and even in artic regions. It should be pointed out that in artic areas because of the large amount of precipitation and particularly snow, it is desirable that the silicone brake fluid be compatible with a certain amount of water, say, up to 6% by weight of water.
In addition, it it desired that the silicone fluid that is to be used as a brake fluid be compatible with the common brake fluids presently on the market, that is, the non-silicone brake fluids, the glycol based polyether fluids. Thus, if by accident some non-silicone brake fluid enters the system or if silicone fluid is added by accident to a hydraulic braking system to replace some glycol based polyether fluid, then it is desirable that the silicone fluid be compatible with the glycol based polyether fluid.
While the above discussion has been directed to the use of a silicone polymer as a brake fluid, it should be mentioned that the above desired properties for a silicone fluid, that is, a silicone fluid having the abovenamed advantages over glycol based polyether fluids, would be a superior hydraulic fluid for use in hydraulic systems. Thus, such a hydraulic system may or may not include a hydraulic reservoir; it would include a mechanical hydraulic activating means which may for instance be a brake pedal to which mechanical pressure is applied; and it would also include a hydraulic activated means which may be the pistons or other types of mechanisms that are activated by the hydraulic pressure in the brake drum shoe or disc brake or other type of hydraulic system assembly. The hydraulic activating means, hydraulic activated means and hydraulic reservoir are all connected by the necessary hydraulic lines. Thus, it is not intended to limit the application of the novel silicone polymer fluid disclosed in this application solely for use in brake hydraulic systems but such a fluid may be used in all types of known hydraulic systems which fluid would have the superior advantages and properties of silicone fluids as well as the specific advantages mentioned above.
Accordingly, it is one object of the present invention to provide for novel silicone polymer fluid having a viscosity that may vary from 2 to 400 centistokes and having a substantial amount of hydrocarbonoxy substituents and hydrocarbonoxy-type substituents on the silicon atoms.
It is another object of the present invention to provide for a novel process for producing a silicone polymer fluid having a viscosity from 2 to 400 centistokes and having a substantial amount of hydrocarbonoxy and hydrocarbonoxy-type substituents on the silicon atom.
It is yet an additional object of the present invention to provide a novel silicone polymer fluid useful as a hydraulic fluid and particularly useful as a hydraulic brake fluid.
It is an additional object of the present invention to provide for a novel silicone polymer fluid having a viscosity of 2 to 400 centistokes at 25.degree. C and which has a compatibility of up to 100% by weight of the fluid of water.
It is still an additional object of the present invention to provide a novel silicone polymer fluid which may be used as a hydraulic fluid and is generally compatible with brake fluids presently sold in commerce.
These and other objects of the present invention are accomplished by means of the invention defined below.